Woven fabric with shape memory element strands

ABSTRACT

The disclosure relates to a woven fabric for use in an implantable medical device. The woven fabric comprises shape memory element strands woven with textile strands. At least one of the shape memory element strands has at least one float of at least five textile strands between binding points.

PRIORITY CLAIM

This application claims the benefit of provisional U.S. PatentApplication Ser. No. 60/906,412, filed Mar. 12, 2007, which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to woven fabrics. More particularly, thepresent invention relates to woven fabrics for implantable medicaldevices.

BACKGROUND OF THE INVENTION

Aneurysms occur in blood vessels in locations where, due to age, diseaseor genetic predisposition, insufficient blood vessel strength orresiliency may cause the blood vessel wall to weaken and/or lose itsshape as blood flows it, resulting in a ballooning or stretching of theblood vessel at the limited strength/resiliency location, thus formingan aneurysmal sac. Left untreated, the blood vessel wall may continue toexpand to the point where the remaining strength of the blood vesselwall cannot hold and the blood vessel will fail at the aneurysmlocation, often with fatal result.

To prevent rupture of an aneurysm, a stent graft of a tubularconstruction may be introduced into the blood vessel and deployed andsecured in a location within the blood vessel such that the stent graftspans the aneurysmal sac. The outer surface of the stent graft, at itsopposed ends, abuts and seals against the interior wall of the bloodvessel at a location where the blood vessel wall has not suffered a lossof strength or resiliency. The stent graft channels the blood flowthrough the hollow interior of the stent graft, thereby reducing, if noteliminating, any stress on the blood vessel wall at the aneurysmal saclocation.

Stent grafts are typically configured by separately forming the graftand the stent(s), and then attaching the graft to stent(s). To attach astent to a graft, the graft is typically inserted into, or pulled over,the stent, and the graft is sewn to the structural components of thestent. Alternatively, the stent may be formed on the graft such that theindividual wires of the stent are threaded through specially providedprojecting fabric loops on the surface of the graft, thereby creatingattachment of the graft to the stent.

Attachment of the graft to the stent in these ways may result in anunneeded bulk. For example, the size of the stent graft, including thewire cage of the stent and the fabric of the graft, as well as the bulkof the connection mechanisms between them, limits the ultimate size of astent graft that can be made that still fits within a catheter forsmaller blood vessel diameter locations. Additionally, known mechanismsfor attachment of the graft to the stent may provide potential sites forseparation between the graft and stent. For example, during manufacture,handling or delivery of the stent graft, the attachment mechanisms maytear or fail, allowing the graft to partially or fully separate from thestent. Furthermore, attachment sites of the stent to graft may permitundesirable leakage of body fluids through the graft structure. Forexample, stents sutured to grafts may create interstices at the site ofsuture, increasing the grafts' porosity.

SUMMARY

In one example, the woven fabric comprises shape memory element strandsand textile strands aligned in a first direction and textile strandsaligned in a second direction. At lease one of the shape memory elementstrands has at least one float of at least five textile strands alignedin the second direction. Preferably, the textile strands comprisepolyester and the shape memory element strands comprise superelasticnitinol wire.

In another example, a method for producing woven fabric is provided. Themethod comprises aligning textile strands and shape memory elementstrands in a first direction, aligning textile strands in a seconddirection, and weaving the shape memory element strands and textilestrands to produce a fabric. At least one of the shape memory elementstrands has at least one float of at least five textile strands in thesecond direction. Preferably, the weave is a tubular double weave. Evenmore preferably, the shape memory element strands comprise superelasticnitinol wires that are heated on a mandrel and cooled prior to weaving.

Other systems, methods, features and advantages will be, or will become,apparent to one with skill in the art upon examination of the followingfigures and detailed description. It is intended that all suchadditional systems, methods, features and advantages be included withinthis description, be within the scope of the invention, and be protectedby the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The woven fabric may be better understood with reference to thefollowing drawings and description. The components in the figures arenot necessarily to scale, emphasis instead being placed uponillustrating the principles of the disclosure. Moreover, in the figures,like referenced numerals designate corresponding parts throughout thedifferent views.

FIGS. 1A and 1B are a schematic representation of one example of wovenfabric weave pattern.

FIG. 2 is a schematic representation of another example of woven fabricweave pattern.

FIGS. 3A, 3B, 3C, and 3D are schematic representations of a furtherexample of woven fabric weave pattern.

FIG. 4 is a schematic representation of yet another woven fabric weavepattern.

FIGS. 5A, 5B, 5C, and 5D are schematic representations of textilestrands weave patterns.

FIG. 6 is a perspective illustration of one example of a medical devicecomprising a woven fabric of the present invention.

DETAILED DESCRIPTION

The present disclosure relates to a fabric comprising shape memoryelement strands and textile strands aligned in a first direction wovenwith textile strands aligned in a second direction such that the shapememory element strands have floats of multiple textile strands.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention pertains. In case of conflict, thepresent document, including definitions, will control. Preferred methodsand materials are described below, although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present disclosure. All publications, patentapplications, patents and other references mentioned herein areincorporated by reference in their entirety. The materials, methods, andexamples disclosed herein are illustrative only and not intended to belimiting.

Definitions

The term “implantable” refers to an ability of a medical device to bepositioned at a location within a body, such as within a body lumen.

The term “strand” as used herein is a generic term for a continuousstrand of material suitable for weaving. For example, strands mayinclude, but are not limited to monofilaments, filaments twistedtogether, fibers spun together or otherwise joined, yarns, roving yarns,crepe yarns, ply yarns, cord yarns, threads, strings, filaments laidtogether without twist, as well as other configurations.

The term “binding point” refers to the intersection of a single strandin a first direction with strands in a second direction. For example, astrand in a first direction may run “over” one or multiple strands in asecond direction, have a binding point, and run “under” one or moresubsequent strands in the second direction.

The term “float” refers to that portion of a strand in a first directionthat extends over or under two or more strands in a second directionwithout a binding point. For example, a strand in a first direction mayhave a binding point with strands in a second direction, then float over5 adjacent strands in the second direction, then have another bindingpoint with strands in the second direction.

The term “alloy” refers to a substance composed of two or more metals orof a metal and a nonmetal intimately united, such as by chemical ormechanical interaction. Alloys can be formed by various methods,including being fused together and dissolving in each other when molten,although molten processing is not a requirement for a material to bewithin the scope of the term “alloy.”

The term “biocompatible” refers to a material that is substantiallynon-toxic in the in vivo environment of its intended use, and that isnot substantially rejected by the patient's physiological system (i.e.,is non-antigenic). This can be gauged by the ability of a material topass the biocompatibility tests set forth in International StandardsOrganization (ISO) Standard No. 10993 and/or the U.S. Pharmacopeia (USP)23 and/or the U.S. Food and Drug Administration (FDA) blue bookmemorandum No. G95-1, entitled “Use of International Standard ISO-10993,Biological Evaluation of Medical Devices Part-1: Evaluation andTesting.” Typically, these tests measure a material's toxicity,infectivity, pyrogenicity, irritation potential, reactivity, hemolyticactivity, carcinogenicity and/or immunogenicity. A biocompatiblestructure or material, when introduced into a majority of patients, willnot cause a significantly adverse, long-lived or escalating biologicalreaction or response, and is distinguished from a mild, transientinflammation which typically accompanies surgery or implantation offoreign objects into a living organism.

The term “prosthesis” means any replacement for a body part or for afunction of that body part; or any device that enhances or addsfunctionality to a physiological system.

The term “endoluminal” describes objects that are found or can be placedinside a lumen or space in the human or animal body. This includeslumens such as blood vessels, parts of the gastrointestinal tract, ductssuch as bile ducts, parts of the respiratory system, etc. “Endoluminalprosthesis” thus describes a prosthesis that can be placed inside one ofthese lumens. The term “about” used with reference to a quantityincludes variations in the recited quantity that are equivalent to thequantity recited, such as an amount that is insubstantially differentfrom a recited quantity for an intended purpose or function.

Weave

The woven fabric may comprise any kind of weave as a primary weave. Forexample, the woven fabric primary weave may include, but is not limitedto, weaves such as plain weaves, basket weaves, rep or rib weaves, twillweaves (e.g., straight twill, reverse twill, herringbone twill), satinweaves, and double weaves (e.g., double-width, tubular double weave,reversed double weave). In one example, the primary weave comprises atubular double layer weave.

Determination of which primary weave is most appropriate may be based ona variety of factors, including intended clinical application, desiredproperties of the woven fabric, weave type, and strand properties suchas the size or denier of the strand and the shape of the strands. Forexample, for percutaneous application, thin fabrics are desired. Suchthin fabrics comprise strands having a low denier. In one example,textile strands in the woven fabric range in size from about 0.1 denierto about 200 denier.

FIG. 1A illustrates one example of a woven fabric with shape memoryelement strands 100 and textile strands 110 in a first direction andtextile strands 115 in a second direction. Textile strands 110 and 115are woven in a primary plain weave characterized by the regularinterlacement of textile strands 110 and 116 in a 1/1 order. That is,each textile strand 110 moves alternatively over and under adjacenttextile strands 115. This plain weave produces the maximum number ofbinding points, and is thus a firm, durable primary weave.

For certain clinical applications, endoluminal prostheses comprisingwoven fabrics having low porosity and low permeability are particularlypreferred. For example, woven fabrics and endoluminal prostheses thatcomprise woven fabrics with integrated shape memory element strandshaving minimal interlacement may provide decreased porosity as comparedto traditional stent-graft structures. Traditional stent grafts areconfigured by suturing the stent to the graft. Attachment of the stentto the graft in this manner may result in undesirable leakage of bodyfluids through the attachment sites of the stent to the graft. Forexample, stents sutured to grafts may create interstices at the site ofsuture, increasing the grafts' porosity.

In one aspect, shape memory element strands 100 woven with a highproportion of floats to binding points may decrease the fabric porosityby minimizing the interlacement of shape memory element strands 100 withtextile strands 115. The shape memory element strands 100 have anover-10/under-6 interlacement configuration, shown in FIG. 1 B. That is,the shape memory element strands 100 float “over” ten textile strands115 and then cross “under” six textile strands 115. The terms “over” and“under” are meant to be relative. For example, the inverse is also true;shape memory element strands 100 float “under” ten textile strands 115and then cross “over” six textile strands 115. This minimalinterlacement with textile strands 115 permits the woven fabric tomaintain low porosity by reducing the number of binding points whilesimultaneously providing the fabric with shape memory characteristics.Additionally, spacing shape memory element strands 100 every sixthstrand in the first direction improves the fabric's low porosity byfurther reducing shape memory element strand binding points whileallowing the fabric to maintain desirable shape memory characteristics.

Alternative examples may have shape memory element strands locatedadjacent one another or have offset binding points to improve the wovenfabric's low porosity and shape memory characteristics. For example,FIG. 2 illustrates woven fabric with shape memory element strands 200and textile strands 210 in a first direction and textile strands 215 ina second direction. Similar to FIG. 1B, textile strands 210 and 215 arewoven in a plain weave and shape memory element strands 200 have anover-10/under-6 interlacement configuration.

Shape memory element strands 200 are woven with two shape memory elementstrands 202 adjacent one another. Adjacent shape memory element strands202 may provide the woven fabric with superior shape memorycharacteristics in the area surrounding adjacent shape memory elementstrands 202. The binding points of shape memory element strands 200occur in a diagonal progression across the fabric, moving systematicallyacross seven textile strands 215. This may serve to distribute shapememory binding points across several different textile strands 115 andfurther reduce fabric porosity.

FIG. 3A depicts a further example of a woven fabric comprising shapememory element strands 300 and textile strands 310 in a first directionand textile strands 315 in a second direction. Shape memory elementstrands 300 are arranged into series 302 comprising eight shape memoryelement strands 300 a-300 h. Each series 302 comprises varying floatsand interlacement configurations as well as differing binding points.For example, 1) the proximal and distal shape memory element strands 300a and 300 h of series 302 have an over-29/under-1 configuration, shownin FIG. 3B; 2) FIG. 3C illustrates intermediate shape memory strands 300b, 300 d, 300 f of series 302 having an over-13/under-2 configuration;and 3) FIG. 3D shows intermediate shape memory strands 300 c, 300 e, 300g of series 302 having an over-27/under-3 configuration. The lengthyfloats of shape memory element strands 300 permit the woven fabric tomaintain an extremely low porosity by reducing the binding points.Organizing shape memory element strands 300 into series 302 provides thefabric with desirable shape memory characteristics while distributingstress across textile strands 310 and 315.

Further examples may have shape memory element strands of varying sizesas compared to textile strands or other shape memory element strands.For example, FIG. 4 illustrates a woven fabric with shape memory elementstrands 400 and textile strands 410 in a first direction and textilestrands 415 in a second direction. Shape memory element strands 401 havea larger size than shape memory element strands 402 and textile strands410 and 415. Shape memory element strands of increased size may permitthe use of fewer shape memory element strands and allow for fewerbinding points between textile strands and shape memory element strands.

Although the woven fabrics in the illustrative figures are shown withtextile strands having a primary weave comprising a plain weave, thetextile strands may have any suitable primary weave. The specificprimary weave will depend on several factors, including theinterlacement pattern of shape memory element strands, type ofapplication, properties of the woven fabric that are desired, and strandproperties such as denier. For example, FIGS. 5A-5D illustrate textilestrands having a primary weave comprising a basket weave 500 a rep weave510, a twill weave 520, and a herringbone weave 530.

Textile Strands

The textile strands may comprise any biocompatible material. The textilestrands may be natural, synthetic, or manufactured. For example,biocompatible materials from which textile strands can be formedinclude, but are not limited to, polyesters, such as poly(ethyleneterephthalate); fluorinated polymers, such as polytetrafluoroethylene(PTFE) and fibers of expanded PTFE; and polyurethanes. In addition,materials that are not inherently biocompatible may be subjected tosurface modifications in order to render the materials biocompatible.Examples of surface modifications include graft polymerization ofbiocompatible polymers from the material surface, coating of the surfacewith a crosslinked biocompatible polymer, chemical modification withbiocompatible functional groups, and immobilization of a compatibilizingagent such as heparin or other substances. Thus, any fibrous materialmay be used to form a textile strand material, provided the finaltextile is biocompatible.

Polymers that can be formed into fibers for making textile strands areparticularly preferred. For example, suitable polymers includepolyethylene, polypropylene, polyaramids, polyacrylonitrile, nylons andcellulose, in addition to polyesters, fluorinated polymers, andpolyurethanes as listed above. Desirably, textile strands comprisebiocompatible polyesters. Even more desirable, textile strands comprisepolyethylene terephthalate and PTFE. A preferred commercial example ofpolyethylene terephthalate especially suited for weaving is Dacron®.These materials are inexpensive, easy to handle, have good physicalcharacterstics and are suitable for clinical application.

Shape Memory Element Strands

Materials used for the shape memory element strands need only bebiocompatible or able to be made biocompatible. Suitable materials forthe shape memory element strands include shape memory metals and shapememory polymers.

Suitable shape memory metals include, for example, TiNi (Nitinol),CuZnAl, and FeNiAl alloys. Particularly preferred are “superelastic”metal alloys. Superelasticity refers to a shape memory metal alloy'sability to spring back to its austenitic form from a stress-inducedmartensite at temperatures above austenite finish temperature. Theaustenite finish temperature refers to the temperature at which thetransformation of a shape memory metal from the martensitic phase to theaustenitic phase completes.

For example, martensite in a nitinol alloy may be stress induced ifstress is applied at a temperature above the nitinol alloy's austenitestart temperature. Since austenite is the stable phase at temperaturesabove austenite finish temperature under no-load conditions, thematerial springs back to its original shape when the stress is removed.This extraordinary elasticity is called superelasticity. In one example,nitinol wire may be in the superelastic condition where the wire hasbeen cold worked at least 40% and given an aging heat treatment atapproximately 500 degrees Celsius for at least 10 minutes. The nitinolwire is in its fully superelastic condition where the use temperature isgreater than the austenite finish temperature of the nitinol wire.

Suitable shape memory polymers include, without limitation, polyethers,polyether esters, polyether amides, polyacrylates, polyamides,polysiloxanes, polyurethanes, polyurethane-ureas, and urethane-butadienecopolymers. See, for example, U.S. Pat. No. 6,720,402 to Langer et al.;U.S. Pat. No. 5,506,300 to Ward et al.; U.S. Pat. No. 5,145,935 toHayashi; and U.S. Pat. No. 5,665,822 to Bitler et al.

Medical Devices

The fabric of the present invention is suitable for use in a variety ofimplantable or insertable medical devices, for example surgically orendoluminally, of any shape or configuration comprising woven fabric.Typical subjects (also referred to herein as “patients”) are vertebratesubjects (i.e., members of the subphylum cordata), including, mammalssuch as cattle, sheep, pigs, goats, horses, dogs, cats and humans.

Typical sites for placement of the medical devices include the coronaryand peripheral vasculature (collectively referred to herein as thevasculature), heart, esophagus, trachea, colon, gastrointestinal tract,biliary tract, urinary tract, bladder, prostate, brain and surgicalsites.

The medical device may be any device that is introduced temporarily orpermanently into the body for the prophylaxis or therapy of a medicalcondition. For example, such medical devices may include, but are notlimited to; endovascular grafts, stent grafts, balloon catheters,meshes, vascular grafts, stent-graft composites, filters (e.g., venacava filters), vascular implants, tissue scaffolds, myocardial plugs,valves (e.g., venous valves), various types of dressings, endoluminalprostheses, vascular supports, or other known biocompatible devices.

One example of the present invention contemplates a tubular implantableprosthesis. Examples of prostheses that may require a tubular designinclude intraluminal prostheses, endovascular grafts, and radiallydeformable support components, such as radially deformable stents.Preferably, a medical device comprising the woven fabric comprises anendoluminal prosthesis.

For example, FIG. 6 depicts an integrated tubular stent-graft 600comprising a woven fabric 610. The woven fabric 610 has radial strands612 and longitudinal strands 614, though the strands need not be radialand longitudinal and may have any suitable orientation. The radialstrands 612 and longitudinal strands 614 may have any suitable weaveconfiguration. For example, the radial strands 612 may comprise shapememory element strands 100 and textile strands 110 and the longitudinalstrands 614 may comprise textile strands 115. Alternatively, the radialstrands 612 of the woven fabric 610 may comprise shape memory elementstrands 300 and textile strands 310 and the longitudinal strands 614 maycomprise textile strands 315. Series 302 of shape memory element strands300 may be located about the proximal integrated stent-graft end 602 anddistal integrated stent-graft end 604 to assist in sealing against abody vessel wall upon implantation.

The medical device may be balloon-expandable or, preferably,self-expanding and may be a bifurcated integrated stent-graft, anintegrated stent-graft configured for any blood vessel includingcoronary arteries and peripheral arteries (e.g., renal, superficialfemoral, carotid, and the like), a urethral integrated stent-graft, abiliary integrated stent-graft, a tracheal integrated stent-graft, agastrointestinal integrated stent-graft, or an esophageal integratedstent-graft, for example.

Method of Manufacture

The present invention is also applicable to methods of producing a wovenfabric comprising shape memory element strands and textile strands. Inone embodiment, the method comprises providing textile strands and shapememory element strands, and weaving the shape memory element strandswith the textile strands to produce a woven fabric.

The fabric may be woven in any way known to one of skill in the art. Forexample, the fabric may be woven on a table loom, a floor loom, ajacquard loom, a counterbalance loom, a jack loom, or an upright loom.Desirably, the fabric is woven on a floor loom.

The fabric may have any configuration possible, but desirably has warpand weft strands. Warp strands preferably include textile strands. Weftstrands preferably include shape memory element strands and textilestrands. In one example, the textile strands range in size from microdenier to about 200 denier.

Prior to weaving, the shape memory element strands may be furtherprepared. For example, shape memory element strands comprising shapememory metals may be wound around a shaped mandrel and heated to atemperature, preferably above the shape memory metal's austenite finishtemperature, to impart a shape memory effect. In one example,superelastic nitinol wire may be cold worked at least 40% and given anaging heat treatment at approximately 500 degrees Celsius for at least10 minutes. Imparting a shape memory effect on the shape memory elementstrands permits a fabric woven with such strands to assume a shapecorresponding to that of the mandrel.

The shape memory element strands may be cooled, preferably to roomtemperature or below room temperature, to improve the shape memoryelement strands' pliability during weaving. For example, shape memoryelement strands comprising shape memory metals may be cooled belowmartensite start temperature. The martensite start temperature is thetemperature at which the martensitic phase begins to form.

Following weaving of the fabric, the fabric may be heated such that theshape memory element strands obtain the shape memory previouslyimparted. For example, shape memory element strands comprising shapememory metals maybe be heated above the metal's austenite starttemperature, preferably above the metal's austenite finish temperatureto obtain the metal's full superelastic effect.

While various aspects and examples have been described, it will beapparent to those of ordinary skill in the art that many more examplesand implementations are possible within the scope of the invention.Accordingly, the invention is not to be restricted except in light ofthe attached claims and their equivalents.

1. A woven fabric suitable for an implantable medical device comprisingshape memory element strands and textile strands aligned in a firstdirection interlaced with textile strands aligned in a second direction,where at least one of the shape memory element strands aligned in thefirst direction has at least one float of at least five textile strandsaligned in the second direction; wherein the woven fabric has reducedbinding points and low porosity.
 2. The woven fabric of claim 1, wherethe textile strands comprise a polymer selected from the groupconsisting of polyester, polypropylene, polyethylene, polyurethane, andpolytetrafluoroethylene, and combinations thereof.
 3. The woven fabricof claim 1, where the textile strands have a denier between about 0.1denier to about 200 denier.
 4. The woven fabric of claim 1, where theshape memory element strands are selected from the group consisting of ashape memory polymer, a shape memory metal, and combinations thereof. 5.The woven fabric of claim 1, where the shape memory element strandscomprise superelastic nitinol wire.
 6. The woven fabric of claim 5,where the superelastic nitinol wire has a diameter between about 70 μmto about 125 μm.
 7. The woven fabric of claim 1, where the shape memoryelement strands in the first direction have at least one float ofbetween six to twelve textile strands in the second direction.
 8. Thewoven fabric of claim 1, where the fabric comprises a primary weaveselected from the group consisting of a plain weave, a basket weave, arep weave, a rib weave, a twill weave, a leno weave, a mock leno weave,a satin weave, a double weave, or a variation thereof.
 9. The wovenfabric of claim 1, where the fabric comprises a tubular double weave.10. The woven fabric of claim 1, further comprising any two or more ofthe following: textile strands comprising a polymer selected from thegroup consisting of polyester, polypropylene, polyethylene,polyurethane, and polytetrafluoroethylene, and combinations thereof;textile strands comprising a denier between about 0.1 denier to about200 denier; shape memory element strands selected from the groupconsisting of a shape memory polymer, a shape memory metal, andcombinations thereof; shape memory element strands comprisingsuperelastic nitinol wire having a diameter between about 70 μm to about125 μm; shape memory element strands in the first direction having atleast one float of between six to twelve textile strands in the seconddirection; and a primary weave selected from the group consisting of aplain weave, a basket weave, a rep weave, a rib weave, a twill weave, aleno weave, a mock leno weave, a satin weave, a double weave, or avariation thereof.
 11. A woven tubular stent-graft comprising shapememory element strands aligned in a first direction and polyesterstrands aligned in the first direction interlaced with textile strandsaligned in a second direction; and a primary weave comprising a tubulardouble weave; where at least one of the shape memory element strands hasat least one float of between six to twelve textile strands aligned inthe second direction and where the woven fabric has reduced bindingpoints and low porosity.
 12. The stent-graft of claim 11, the shapememory element strands comprising a superelastic nitinol wire having adiameter between about 70 μm to about 125 μm and the textile strandscomprising polyester having a denier between about microdenier to about200 denier.